B772, San Francisco CA USA, 2013

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Summary

On 6 July 2013, an Asiana Boeing 777-200 descended below the visual glidepath on short finals at San Francisco after the pilots failed to notice that their actions had reduced thrust to idle. Upon late recognition that the aircraft was too low and slow, they were unable to recover before the aircraft hit the sea wall and the tail detached. Control was lost and the fuselage eventually hit the ground. A few occupants were ejected at impact but most managed to evacuate subsequently and before fire took hold. The Probable Cause of the accident was determined to be the mismanagement of the aircraft by the pilots.

Description

On 6 July 2013, a Boeing 777-200ER (HL7742) being operated by Asiana Airlines, on a scheduled passenger flight (214) from Seoul Incheon to San Francisco, crashed within the airport perimeter shortly before completing a landing in day VMC after the aircraft had hit the sea wall situated prior to the runway and the tail had detached. The aircraft was destroyed by the impact and a post crash fire. Three of the 307 occupants were fatally injured, 49 sustained serious injuries and 138 sustained minor injuries. The other 117 occupants were uninjured.

It was established that the aircraft had been radar-vectored towards a straight-in visual approach to runway 28L. The Instrument Landing System (ILS) was out of service and, in the prevailing excellent in flight visibility, the Automatic Terminal Information Service (ATIS) had advised that a visual approach should be expected. The ILS LOC was radiating normally and the installed Visual Approach Slope Indicator Systems were working. The flight crew consisted of a trainee Captain acting as PF and in the left hand seat accompanied by a Training Captain acting as PM and designated as aircraft commander in the right hand seat. The relief First Officer from the augmented crew was occupying one of the supernumerary seats in the flight deck but the relief Captain had left the flight deck. The PF advised that he intended to keep the AP engaged and capture the LOC whilst managing the descent using the AFCS. The MDA and Missed Approach stop altitude for the LOC procedure were set.

The aircraft had intercepted the extended centreline at about 14nm from the runway threshold slightly above the nominal 3° glidepath. An ATC instruction to maintain 180 KIAS until 5nm from the runway was accepted but the rate of descent was insufficient so that by the time the aircraft reached the 5nm point, it was well above the 3° glidepath. Difficulty in managing the descent continued and in an attempt to increase the rate of descent, the PF (inappropriately) selected FLCH SPD mode and the A/T changed from SPD mode to THR mode. These actions resulted in the commencement of a climb because the aircraft was, by this time, below 2000 feet and therefore below the selected altitude (for the LOC missed approach procedure) of 3000 feet. In response to the commencement of the unwanted climb, the PF disconnected the AP and moved the thrust levers to flight idle. The latter action caused the A/T to change to HOLD mode in which it no longer controls airspeed. The PF then pitched the aircraft down and increased the descent rate. Neither the PF, the PM nor the Observing First Officer noticed the A/T mode changing to HOLD.

Shortly after this, recorded flight data showed that the aircraft had passed 1300 feet at a range of 2.9nm from the threshold and with an approximate 1000fpm rate of descent. The PAPI would have indicated all white lights at this time. As the aircraft reached 500 feet aal, the point at which Asiana SOPs required that the approach must be stabilised, the PAPI would have confirmed that the aircraft was slightly above the intended height but although the airspeed, which had been decreasing rapidly, had just reached the calculated Vapp of 137KIAS (based on a Vref of 132 KIAS), the thrust levers were still set to flight idle and the descent rate was around 1200fpm, the latter being far higher than the rate needed to maintain the necessary vertical profile - about 700fpm. This situation indicated that the approach did not meet the established Asiana criteria for a stabilised approach and that a go around should be commenced immediately, but it was not.

From there on, the approach “became increasingly unstabilised” as descent below the required vertical profile continued. The PAPI display would have transitioned to three and then four red lights, indicating an increasing deviation below the indicative glidepath. With the A/T engaged and only flight idle thrust commanded, airspeed continued to decrease until, at about 200 feet, the flight crew at last recognised their situation. However, there was no immediate attempt to initiate a go around and, by the time thrust was added and the pitch increased, the aircraft was less than 100 feet agl and in a position where the low energy state of the aircraft meant that it was no longer possible to successfully transition to one. As the airspeed reached 104 KCAS, and the aircraft was at 46 feet agl, stick shaker activation began. This was followed by a call - from the PM - for a go around, the first and only such call by any crew member, at 29 feet agl. 2.5 seconds later, the main landing gear and the aft fuselage struck the seawall situated just prior to the landing threshold with the airspeed recorded as 106 KCAS. The impact led to the tail of the aircraft breaking off at the aft pressure bulkhead. The remainder of the aircraft then “slid along the runway, lifted partially into the air, spun anticlockwise through about 330°” before impacting the ground to the left of the runway a final time.

The final stages of the approach reconstructed as a vertical profile from recorded flight data are shown below. The two photographs below show the fuselage following the fire that rapidly took hold and the location of the main wreckage relative to the runway threshold, the adjacent sea wall and the detached tail.

An annotated vertical profile of the final 40 seconds of the flight (reproduced from the Official Report)

Soon after the fuselage and its still-attached wings came to a stop, a fire started in the separated right engine which had come to rest next to the right hand side of the fuselage.

Aerial view of the wreckage (reproduced from the Official Report)

The Cabin Manager, having sought instructions from the flight crew as to whether an evacuation should be ordered in the absence of any prior such instruction directly from the flight crew, was told by them that no evacuation was necessary and that passengers should remain seated. Whilst she was making a PA to that effect, a junior member of the cabin crew at the rear of the aircraft, was already aware from the situation apparent from that position that an immediate evacuation was imperative. He asked a colleague to go and stop the PA being made by Cabin Manager and made one to do so in both Korean and English and it began, with the Cabin Manager complying.

Almost all the passengers successfully self-evacuated. As the fire spread into the fuselage, Rescue and Fire Fighting Services personnel entered the aircraft and recovered five passengers who had been unable to evacuate unaided because of their injuries. One of these passengers subsequently died.

Impact forces, which “far exceeded design certification limits”, resulted in the inflation of two emergency evacuation slides inside the passenger cabin causing injury to and temporarily trapping two of the cabin crew. Two of the passengers and four of the cabin crew were ejected from the aircraft during the impact sequence. The two passengers were both fatally injured as a result and the four cabin crew all sustained serious injuries. Neither of the two ejected passengers, one of whom was later run over by two RFFS vehicles, were wearing their seatbelts and the Investigation concluded that their ejection was attributed entirely to that fact and that they would otherwise have remained in the cabin and survived. The four cabin crew were all wearing their full seat harnesses but were ejected as a result of the destruction of the aft galley where they had been seated.

The remains of the fuselage showing the eight exits used in the evacuation (Source: NTSB)

The Operation of the Aircraft

The Investigation found no evidence of any pre-accident unserviceabilty which was relevant to the conduct of the approach. The way the aircraft had been operated was therefore examined in terms of the way the flight crew had performed and the context for that performance.

It was established that the Training Captain who had been the pilot in command for the accident flight had been employed by Asiana since leaving the Korean Air Force. He had been promoted to the rank of Captain in 2001 on the Boeing 767 and had transferred to the Boeing 777 fleet in that rank in 2008. He had completed Asiana requirements for promotion to Training Captain, referred to on the Investigation Report as "Instructor Pilot", May and June 2013, becoming qualified as such on 12 June 2013. The accident flight was the first time he had supervised a trainee pilot.

The Investigation noted the existence of the Asiana Flight Operations Manual (FOM) and the Asiana Pilot Operating Manual (POM), the former laying down general guidance and procedures and the latter more detailed instructions. The Investigation established that where the POM was more restrictive than either the FOM or the Boeing FCOM or FCTM, it took precedence. The content of the POM relevant to the conduct of the accident approach was noted to include the following:

Flight crew must always monitor airplane course, vertical path, and speed; verify manually selected or automatic AFDS changes and when selecting a value on the MCP, verify that the respective value changes on the flight instruments.

That flight crew should use the FMA to verify mode changes for the A/P, F/D, and A/T and that to “call out loudly and clearly to the changes on the FMA and thrust mode display when they occur are a good CRM practice.”

“Operations by A/P and A/T have preference to improve safety, to reduce workload and to enhance operational capability.”

“Operating within terminal areas where air traffic congestion could be expected, the PF and the PM [should] make full use of A/P and A/T.”

Flight crew should use the A/P and A/T together and recommended use of A/T during all phases of flight, including manual flight.

The PF should notify the PM when disengaging or disconnecting the A/P and/or A/T by calling out “manual flight” upon disconnecting the A/P and “A/T disconnect” upon disconnecting A/T and the PM should verify that the change is indicated by a change in AFDS status or mode annunciation on the FMA and then [also] call out the change.

Under “Crew duties”, it is stated that whilst manipulating the controls and switches on the MCP is the PF’s responsibility, "when flying manually, the PF should direct the PM to make changes on the MCP".

The pilot who is in charge of “flight mode change” must call out accomplishment of a mode change, and the other pilot must respond with a confirmation and that "the PM should call out every FMA change".

The Investigation also noted that, in respect of the use of FLCH SPD mode, the FCTM stated that “non-ILS approaches are normally flown using VNAV, V/S, or [flightpath angle] FPA pitch modes. The use of FLCH is not recommended after the FAF.”

The Investigation was told by the Asiana Boeing 777 fleet Chief Pilot that:

the airline recommended using as much automation as possible.

it was permissible for Asiana pilots to disengage the AP above 1,000 ft, but turning the AP off at 8 nm from the airport and at 2,800 ft, for example, would not be recommended.

the used of FLCH SPD on final approach "not recommended" although there was no explicit requirement to that effect.

when executing a manually flown visual approach, it was mandatory to have the A/T on for final approach.

The Investigation was told by two Asiana Captains with previous experience at other airlines that "most Asiana First Officers preferred to make automated landings or to leave the A/P engaged to 1,000 ft agl or lower before taking over and landing manually". An Asiana contract simulator instructor stated that manual flying was a “big scare for everybody” and that he believed that "pilots avoided flying manually because of concern that they might do something wrong and the company would blame them if they performed a go-around or had a hard landing that was captured by onboard flight data monitoring devices". This person also noted stated that "manual flying training that included the approximate power settings and pitch attitudes required to achieve a 3° glidepath was not in the training syllabus".

In specific reference to visual approaches, the POM was found to describe how to set up downwind, base, and final legs using the FMC arrival page and how to use distance from the runway end and timing techniques to fly the visual traffic pattern. It also stated that on final approach,, the recommended approach path angle was 2.5° to 3° which was equivalent to about 300 ft of height for each mile from the runway.

And in respect of stabilised approaches, the POM stated, “every flight crewmember must confirm and monitor a stabilized approach”, and “if a stabilized approach is not established, go-around” accompanied by a note that stated “deciding to make Go-Around does not mean that the procedure has been done wrong, but it means that crews follow[ed] the company safety policy and executed safety procedure normally.”

The Investigation identified a number of 'Safety Issues which, in relation to the way the approach was flown included the following:

The flight crew did not consistently adhere to Asiana’s SOPs involving selections and callouts pertaining to the autoflight system’s mode control panel.

The PF had a faulty mental model of the airplane’s automation logic.

The PM did not have the opportunity during his instructor training to supervise and instruct a trainee during line operations while being observed by an experienced instructor.

The use of flight directors during visual approaches flown by Asiana pilots amounted to no more than (flawed) informal practice.

Asiana’s automation policy emphasised the full use of all automation and did not encourage manual flight during line operations.

The low airspeed alerting system fitted to the aircraft was designed to provide pilots with redundant aural and visual warning of impending hazardous low-airspeed in the cruise and was not adequately tailored to reflect conditions that may be important during other flight phases including approach.

Conclusions in respect of the handling of the accident aircraft on the approach included the following:

Although the instrument landing system glideslope was out of service, the lack of a glideslope should not have precluded the pilots’ successful completion of a visual approach.

The flight crew mismanaged the airplane’s vertical profile during the initial approach, which resulted in the airplane being well above the desired glidepath when it reached the 5 nautical mile point, and this increased the difficulty of achieving a stabilized approach.

The flight crew’s mismanagement of the airplane’s vertical profile during the initial approach led to a period of increased workload that reduced the pilot monitoring’s awareness of the pilot flying’s actions around the time of the unintended deactivation of automatic airspeed control.

The flight crew was experiencing fatigue, which likely degraded their performance during the approach.

Nonstandard communication and coordination between the pilot flying and the pilot monitoring when making selections on the mode control panel to control the autopilot flight director system (AFDS) and autothrottle (A/T) likely resulted, at least in part, from role confusion and subsequently degraded their awareness of AFDS and A/T modes.

The delayed initiation of a go-around by the pilot flying and the pilot monitoring after they became aware of the airplane’s low path and airspeed likely resulted from a combination of surprise, nonstandard communication, and role confusion.

As a result of complexities in the 777 AFCS and inadequacies in related training and documentation, the pilot flying had an inaccurate understanding of how the autopilot flight director system and autothrottle interacted to control airspeed, which led to his inadvertent deactivation of automatic airspeed control.

If the autothrottle automatic engagement function (wakeup), or a system with similar functionality, had been available during the final approach, it would likely have activated and increased power about 20 seconds before impact, which may have prevented the accident.

If the pilot monitoring had supervised a trainee pilot in operational service during his instructor training, he would likely have been better prepared to promptly intervene when needed to ensure effective management of the airplane’s flightpath.

If Asiana Airlines had not allowed an informal practice of keeping the pilot monitoring’s (PM) flight director (F/D) on during a visual approach, the PM would likely have switched off both F/Ds, which would have corrected the unintended deactivation of automatic airspeed control.

A more general concern was also identified about the way the A/T HOLD mode was likely to be understood by pilots. In this context, it was found that the FAA had required Boeing to include the following text in Boeing 787 Aircraft Flight Manual (AFM):

"During a descent in FLCH mode or VNAV SPD mode, the A/T may activate in HOLD mode. When in HOLD mode, the A/T will not wake up even during large deviations from target speed and does not support stall protection."

It was, however, noted that although the Boeing 777 A/T functions in exactly the same way as that on the 787, similar text did not appear in the FAA-approved 777 AFM.

It was also considered that a context-dependent low energy alert would help pilots successfully recover from unexpected low-energy situations like the situation encountered by the accident pilots.

Cabin Crew Performance

The evidence available to the Investigation indicated that the cabin crew had performed their pre landing checks on what had been a difficult flight with diligence. It was also considered that the action of the junior cabin crew member in initiating an emergency evacuation contrary to aircraft commander's order for the passengers to remain seated had been "appropriate".

Air Traffic Control Service

Whilst there was no suggestion that any action by Air Traffic Control had had any effect at all on either the approach or the accident outcome, the Investigation did review the Minimum Safe Altitude Warning (MSAW) installation at San Francisco. This was found to include coverage of the approach to the accident runway and this had been configured in two sectors, the first beginning at the runway threshold and extending out to 2 miles and the second from that point out to 5 miles. Recorded radar data confirmed that the system had operated as expected and no Alerts had been generated. However, whilst the reason for this in the outer sector was that the alert threshold was not breached, the Alerts which would otherwise have occurred within the final 2 miles "were suppressed because an aircraft in this area was expected to be in close proximity to terrain". No comment was made on this finding except to note that a simulation subsequently conducted had indicated that even if the MSAW configuration in use had been set so that the outer sector began at a point 1 mile from the runway threshold instead of 2 miles, there would still have been no Alert generated for the accident aircraft approach.

Emergency Services Response

The direction of the emergency services' response to the accident raised a number of concerns in respect of training, staffing and communications which are discussed in detail in the Official Report.

Crashworthiness and Survivability

In the context of a survivable accident, it was noted that the dynamics of the impact sequence were such that occupants had first been thrown forward and had then experienced a significant lateral force to the left. It was considered that "current FAA dynamic seat certification requirements would likely not approximate the forces encountered in this accident" and concluded that "the mechanism which leads to the significant number of serious injuries to the high thoracic spine in this accident is poorly understood." It was also noted that although the forces experienced by the stowed evacuation slides during the impact sequence had been "far in excess of their current certification requirements", the location of cabin crew near to them and the consequences of that, which included the temporary trapping of two of them, indicated that there was a case for a regulatory review of those requirements.

The Post Crash Fire

The Investigation found no evidence that the post crash fire had been fuel fed. Rather, the oil tank of the detached right hand engine, positioned near to the fuselage was "breached and partially melted" and "thermal damage signatures around the oil tank were consistent with an oil-fed fire". However, whilst the fuselage near the engine was severely heat damaged, there had been no penetration of fire through the skin. Rather, it was concluded that the fire had spread to the cabin from the under-floor cargo bay taking a path "up an environmental control system riser duct bay......and into the overhead area".

The Probable Cause of the accident was determined as "the flight crew’s mismanagement of the airplane’s descent during the visual approach, the pilot flying’s unintended deactivation of automatic airspeed control, the flight crew’s inadequate monitoring of airspeed, and the flight crew’s delayed execution of a go-around after they became aware that the airplane was below acceptable glidepath and airspeed tolerances".

It was further determined that the following had Contributed to the accident:

the complexities of the autothrottle and autopilot flight director systems that were inadequately described in Boeing’s documentation and Asiana’s pilot training, which increased the likelihood of mode error

the flight crew’s non-standard communication and coordination regarding the use of the autothrottle and autopilot flight director systems

the pilot flying’s inadequate training on the planning and executing of visual approaches

the pilot monitoring/instructor pilot’s inadequate supervision of the pilot flying

flight crew fatigue which likely degraded their performance

Safety Action notified to the Board whilst the Investigation was in progress included major changes to pilot training by Asiana and significant enhancements to support improved emergency services response to aircraft accidents at San Francisco Airport by the City and County of San Francisco.

A total of 27 Safety Recommendations were made as a result of the Investigation.
Four were made in respect of the aircraft operating procedures and the related pilot training process at Asiana Airlines and were as follows:

that Asiana Airlines reinforce, through your pilot training programs, flight crew adherence to standard operating procedures involving making inputs to the operation of autoflight system controls on the 777 mode control panel and the performance of related callouts. [A-14-52]

that Asiana Airlines revise your flight instructor operating experience (OE) qualification criteria to ensure that all instructor candidates are supervised and observed by a more experienced instructor during OE or line training until the new instructor demonstrates proficiency in the instructor role. [A-14-53]

that Asiana Airlines issue guidance in the Boeing 777 Pilot Operating Manual that after disconnecting the autopilot on a visual approach, if flight director guidance is not being followed, both flight director switches should be turned off. [A-14-54]

that Asiana Airlines modify your automation policy to provide for more manual flight, both in training and in line operations, to improve pilot proficiency. [A-14-55]

Six were made in respect of the operation of the accident aircraft type in general and were as follows:

that the Federal Aviation Administration, once the enhanced Boeing 777 training has been developed as requested in Safety Recommendation A-14-37, require operators and training providers to provide this training to 777 pilots. [A-14-38]

that the Federal Aviation Administration require Boeing to revise its 777 Flight Crew Training Manual stall protection demonstration to include an explanation and demonstration of the circumstances in which the autothrottle does not provide low speed protection. [A14-39]

that the Federal Aviation Administration, once the revision to the Boeing 777 Flight Crew Training Manual has been completed, as requested in Safety Recommendation A-14-39, require operators and training providers to incorporate the revised stall protection demonstration in their training. [A-14-40]

that the Federal Aviation Administration convene a special certification design review of how the Boeing 777 automatic flight control system controls airspeed and use the results of that evaluation to develop guidance that will help manufacturers improve the intuitiveness of existing and future interfaces between flight crews and autoflight systems. [A-14-42]

that Boeing revise the 777 Flight Crew Operating Manual to include a specific statement that when the autopilot is off and both flight director switches are turned off, the autothrottle mode goes to speed (SPD) mode and maintains the mode control panel-selected speed. [A-14-56]

Three were made in respect of the operation of automated transport aircraft generally and the application of any guidance to Boeing wide body aircraft types and were as follows:

that the Federal Aviation Administration convene an expert panel (including members with expertise in human factors, training, and flight operations) to evaluate methods for training flight crews to understand the functionality of automated systems for flightpath management, identify the most effective training methods, and revise training guidance for operators in this area. [A-14-41]

that the Federal Aviation Administration task a panel of human factors, aviation operations, and aircraft design specialists, such as the Avionics Systems Harmonization Working Group, to develop design of context-dependent low energy alerting systems for airplanes engaged in commercial operations and establish requirements for such systems, based on the guidance developed by the panel. [A-14-43]

that Boeing, using the guidance developed by the low-energy alerting system panel created in accordance with recommendation A-14-43, develop and evaluate a modification to Boeing wide-body automatic flight control systems to help ensure that the aircraft energy state remains at or above the minimum desired energy condition during any portion of the flight. [A-14-57]

Three were made in respect of the crashworthiness of the accident aircraft type and the relationship of this to the protection of occupants in survivable accidents and were as follows:

that the Federal Aviation Administration conduct research that examines the injury potential to occupants in accidents with significant lateral forces, and if the research deems it necessary, implement regulations to mitigate the hazards identified. [A-14-44]

that the Federal Aviation Administration conduct research to identify the mechanism that produces high thoracic spinal injuries in commercial aviation accidents, and if the research deems it necessary, implement regulations to mitigate the hazards identified. [A-14-45]

that the Federal Aviation Administration analyze in conjunction with slide raft manufacturers the information obtained in this accident investigation and evaluate the adequacy of slide and slide/raft certification standards and test methods specified in Federal Aviation Administration regulations and guidance materials. If appropriate, modify certification standards and test methods for future slide and slide/raft design based on the results of this evaluation. [A-14-46]

Eleven were made in respect of the response to the accident by the emergency services and were as follows:

that the Federal Aviation Administration work with the Aircraft Rescue and Firefighting Working Group and equipment manufacturers to develop and distribute more specific policies and guidance about when, how, and where to use the high-reach extendable turret’s unique capabilities. [A-14-47]

that the Federal Aviation Administration, once the minimum staffing level has been developed by the Aircraft Fire and Rescue (ARFF) Working Group, as requested in Safety Recommendation A-14-60, amend 14 Code of Federal Regulations 139.319(j) to require a minimum ARFF staffing level that would allow exterior firefighting and rapid entry into an airplane to perform interior firefighting and rescue of passengers and crewmembers. [A-14-48]

that the Federal Aviation Administration work with the Aircraft Rescue and Firefighting (ARFF) Working Group to develop policy guidance and training materials to ensure that all airport and mutual aid firefighting officers placed in command at the scene of an aircraft accident have at least a minimum level of ARFF training. [A-14-49]

that the Federal Aviation Administration issue a CertAlert to all Part 139 airports to distribute the information contained in the Federal Aviation Administration’s (FAA) legal interpretation of 14 CFR 139.319 that requires all personnel assigned to aircraft rescue and firefighting duties to meet the initial and recurrent training and live-fire drill requirements and clarify how the FAA will enforce this regulation. [A-14-50]

that the Federal Aviation Administration conduct a special inspection of San Francisco International Airport’s emergency procedures manual and work closely with the airport to ensure that the airport meets its obligations under Part 139.325. [A-14-51]

that the Aircraft Rescue and Firefighting Working Group work with the Federal Aviation Administration and equipment manufacturers to develop and distribute more specific policies and guidance about when, how, and where to use the high-reach extendable turret’s unique capabilities. [A-14-58]

that the Aircraft Rescue and Firefighting Working Group work with medical and medicolegal professional organizations to develop and distribute guidance on task prioritization for responding aircraft rescue and firefighting (ARFF) personnel that includes recommended best practices to avoid striking or rolling over seriously injured or deceased persons with ARFF vehicles in a mass casualty situation. [A-14-59]

that the Aircraft Rescue and Firefighting Working Group develop a minimum aircraft rescue and firefighting staffing level that would allow exterior firefighting and rapid entry into an airplane to perform interior firefighting and rescue of passengers and crewmembers. [A-14-60]

that the Aircraft Rescue and Firefighting Working Group develop and distribute, in conjunction with the Federal Aviation Administration, guidance and training materials to ensure that all airport and mutual aid firefighting officers placed in command at the scene of an aircraft accident have at least a minimum level of airport rescue and firefighting training. [A-14-61]

that the City and County of San Francisco routinely integrate the use of all San Francisco Fire Department medical and firefighting vehicles in future disaster drills and preparatory exercises. [A-14-62]

that the City and County of San Francisco implement solutions to the communications deficiencies identified in ICF International’s after-action report as soon as practicable. [A-14-63]